Many modern operating systems (OS's) use the Advanced Configuration and Power Interface (ACPI) standard, e.g., Rev. 3.0b, published Oct. 10, 2006, for optimizing system power. An ACPI implementation allows a processor core to be in different power-consumption states, generally referred to as so-called C1 to Cn states. When a core is active, it runs at a so-called C0 state, and when the core is idle it may be placed in a core low power state, a so-called core non-zero C-state (e.g., C1-C6 states).
In addition to power-saving states, performance states or so-called P-states are also provided in ACPI. These performance states may allow control of performance-power levels while a core is in an active (C0) state. In general, multiple P-states may be available, namely from P0-Pn, where P0 corresponds to a maximum rated frequency for the core, while each P-state, e.g., P1-Pn, operates the core at lower performance levels.
Turbo mode is a mechanism that allows one or more cores of a processor to operate at higher than this maximum rated frequency, when there is enough power and thermal budget available. But as the power consumption on a core increases, its thermal dissipation also increases, which makes the core hotter than when it is not running in turbo mode. When a core becomes hotter, a thermal throttling mechanism initiates to reduce thermal dissipation by reducing the frequency of the core. The amount of time a core can be in turbo mode in general thus depends on two factors: (1) base temperature of the core when a job is assigned to it with turbo mode enabled; and (2) time taken to reach the thermal trip point of the thermal throttling mechanism.